Bone fixing device

ABSTRACT

A bone fixing device and in particular a device for stabilizing cervical vertebrae is provided, (with) a plate ( 2, 200 ) with at least one recess ( 5 ) for guiding through a section ( 15, 61, 62 ) of a bone screw ( 6, 60 ), a connecting element ( 20, 30 ), displaceable in the recess, for connecting the bone screw to the plate and a securing device ( 10, 11 ) for securing the connecting element against falling out of the recess.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of application Ser. No. 10/279,196,filed Oct. 23, 2002 now U.S. Pat. No. 7,771,458, which claims priorityto and the benefit of German Patent Application No. 101 52 094.8 filedon Oct. 23, 2001, the disclosures of which are fully incorporated hereinby reference.

BACKGROUND

The invention relates to a bone fixing device and in a particularapplication to a device for stabilising cervical vertebrae.

A device especially for stabilising cervical vertebrae is known,comprising a plate with at least one bore, having an M-thread, and abone screw for screwing into the plate. The bone screw has a threadsection, having a bone thread, for screwing into the bone and anadjoining thread section with an outer M-thread. In operation the bonescrew is guided through the bore and screwed into the bone. Then thesecond thread section is screwed into the plate. Because the threadpitches are different there is a danger that the bone screw will therebybe loosened from its seat.

From WO 96/05778 a cervical vertebrae stabilising system is known whichhas a plate with at least one recess, a bone screw with a bone threadsection and an adjoining M-thread section and a radial projectionprovided between the bone thread section and the M-thread section, andalso a nut cooperating with the M-thread section. With this known devicefirst the bone screw is screwed into the bone, then the plate with therecess is guided over the M-thread section until it rests against theradial projection and then the nut is inserted into the recess andscrewed on to the M-thread section to fix it. The recess can beconstructed as an elongated hole.

From WO 00/18312 a stabilising device for the spinal column is known,which has a plate with at least one recess, a bone screw with a bonethread section and an M-thread section and a projection provided betweenthese sections and with a plain washer located on top of the edge of therecess, and also a nut which is screwed on over the M-thread section ofthe bone screw until it is adjacent to the shim. The plain washer has alateral recess, so the bone screw can take up various angles.

The known systems are suitable for particular applications in each case.With the first mentioned device, for instance, the plate must always beput in first and then the screw screwed in. With the device known fromWO 96/05778, on the other hand, the screw has to be screwed in first andthen the plate placed on top. Additionally, with this device it is notpossible to change the angle of the screw. The device known from WO00/18312 admittedly allows different angles of the bone screw, butadjustment of the plate in the longitudinal direction is possible onlyto a limited extent. Additionally, this device has a relatively highconstruction.

SUMMARY

The object of the invention is to provide a bone fixing device and inparticular a device for stabilising cervical vertebrae, which isimproved with respect to adjustability and breadth of applicationcompared with the known devices.

This object is achieved by a bone fixing device according to patentclaim 1. Further developments of the invention are cited in thedependent claims.

The invention has the particular advantage of a modular system, whichconsiderably enlarges the breadth of application. The apparatusaccording to the invention is not only usable for cervical vertebraestabilisation, but also as a bone fixing device for fixing broken bones,e.g. tubular bones. The invention further enables the surgeon in theoperating room to make a decision, adapted to the circumstances of theindividual case, as to whether the screws should be inserted first andthen the plate placed over them and fixed or whether the plate should beput in first and then the bone screws screwed in through the recesses ofthe plate. The invention further allows monoaxial and polyaxial screwsto be used together with one plate or even both types of screws next toone another. In this way adjustment of the angle of the screws to theplate and positioning of the screws for adjusting their longitudinaldistance is possible independently for each screw.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention emerge from thedescription of embodiment examples with the aid of the figures.

FIG. 1 shows a perspective view of the bone fixing device according to afirst embodiment.

FIG. 2 shows a horizontal projection on to the plate of the bone fixingdevice according to FIG. 1.

FIG. 3 shows a perspective exploded representation of the bone screw andthe plain washer of the bone fixing device according to FIG. 1.

FIG. 4 shows a section through a part of the bone fixing deviceaccording to FIG. 1.

FIG. 5 shows a perspective exploded representation of a bone fixingdevice according to a second embodiment.

FIG. 6 shows a section through the bone fixing device according to thesecond embodiment.

FIG. 7 shows a perspective exploded representation of a bone fixingdevice according to a third embodiment.

FIG. 8 shows a section through the bone fixing device of the thirdembodiment.

FIG. 9 shows a perspective exploded representation of a bone fixingdevice according to a fourth embodiment.

FIG. 10 shows a section through the bone fixing device according to thefourth embodiment.

FIG. 11 shows a perspective representation of a modification of the bonescrew of the preceding embodiments.

FIG. 12 shows a modified form of the plate of the bone fixing device ofthe preceding embodiments.

DETAILED DESCRIPTION

As can be seen from FIGS. 1 to 4, the bone fixing device 1 has asubstantially rectangular plate 2 with rounded corners. For furtherdescription the midline of the plate running in the longitudinaldirection of the rectangle is designated as D and the midline runningperpendicularly to it in the crosswise direction as C. The plate has afirst end 3 and a second end 4 opposite this with recesses 5, providedin each case near the ends, for receiving bone screws. Each recess 5 hasa first area 5 a with a first diameter d₁ in a direction perpendicularto midline D and a second area 5 b with a second diameter d₂ in adirection perpendicular to midline D, wherein the second diameter d₂ islarger than the first diameter d₁. The total diameter of the recess 5 inthe longitudinal direction, in other words on midline D, is larger thanthe second diameter d₂. Areas 5 a and 5 b are formed, for example, by anelongated hole, the small diameter of which corresponds to the diameterof area 5 a, and an additional bore with the larger diameter d₂ of area5 b. Areas 5 a and 5 b are arranged on the plate in such a way that area5 b is facing away from the respective end 3 or 4 of the plate andpoints towards midline C. On the upper side 2 a of the plate 2 facingaway from the shank of the bone screw 6 in a state of use each recess Shas an indentation 7 for receiving a subsequently described connectingelement.

The plate 2 further has, bordering on areas 5 b of the recesses 5,thread bores 8, located opposite one another, with an indentation 9 forscrewing in screws 10 with a head 11, which are constructed, forexample, as slit screws. The thread bore 8 is provided at such adistance from area 5 b of the recess 5, and the indentation 9 and thehead 11 of the screw 10 are dimensioned in such a way, that in thescrewed in state the head 11 projects just a little into the area of theindentation 7 in area 5 b of the recess 5 and thus limits thecross-section of the indentation 7.

As can be seen in particular from FIGS. 1, 3 and 4, for connecting thebone screw to the plate 2 the bone fixing device has a connectingelement in the form of a supporting element or shaped part, constructedas sleeve-shaped, called hereinafter a plain washer 20. The plain washer20 has a hollow cylindrical section 21, the length of which is slightlygreater than the thickness of the plate in the area of the recess 5. Onthe side arranged in the state inserted into the plate 2 on the upperside 2 a of the plate the plain washer 20 is constructed with a section22, shaped as a hollow spherical segment, the outer diameter of which issmaller than the diameter of the indentation 7 crosswise to midline D,but greater than the diameter d₂ of the second area 5 b, so in theinserted state the plain washer 20 with the area 22 lies on top at theedge of the indentation 7. Section 22, shaped as a hollow sphericalsegment, is constructed on the inside with a spherical radiuscorresponding to the spherical radius of a head 6 a of the bone screw 6shaped as a spherical segment. At the end facing away from the section22, shaped as a hollow spherical segment, the plain washer 20 has aring-shaped projection 23, the outer diameter of which is larger thanthe diameter d₁ of the first area 5 a of the recess 5 and smaller thanthe diameter d₂ of the second area 5 b of the recess 5. The plain washer20 is thus so dimensioned that it can be inserted through area 5 b withthe larger diameter d₂ of the recess 5 into the recess 5 and can bedisplaced in the longitudinal direction of the plate in the indentation7 until it is in area 5 a, from which it cannot fall out. Theindentation 7 forms a guide for the plain washer.

The bone fixing device 1 of the first embodiment further has the bonescrew 6, which in this embodiment is constructed in one piece, with ashank 15 with a bone thread for screwing into the bone and with the head6 a, which is shaped as a spherical segment and firmly connected to theshank and on its upper side has a means 16, e.g. one of more slits, forbringing into engagement with a screwing-in tool.

In operation first the plain washer 20 is guided in through area 5 b ofthe recess 5, so the section 22, shaped as a hollow spherical segment,is located on the upper side 2 a of the plate. Then the plain washer ispushed in the direction of area 5 a, wherein the underside of section22, shaped as a hollow spherical segment, is lying on top in theindentation 7. In area 5 a with the smaller diameter d₁ the plain washer20 is held against falling out owing to the larger diameter of section22, shaped as a hollow spherical segment, and the projection 23. Thenthe securing screw 9 is screwed into the bore 8. The edge of the head 11of the securing screw 9 therein projects, as can be seen in particularfrom FIGS. 1, 2 and 4, slightly into the area of the indentation 7 ofthe recess 5 and thus limits the diameter of the indentation 7 in area 5b, securing the plain washer 20 from falling out after it has beeninserted. However, the plain washer 20 is still therein displaceable inthe longitudinal direction in the recess 5 and is pushed to the exactposition desired. Then the bone screws 6 with the thread shank 15 withthe bone thread are guided through the plain washer and screwed into thebone.

During an operation the surgeon uses the plate with already insertedplain washers 20, secured against falling out by the screws 9, whichthus in each case form an integrated shaped part, and holds them againstthe bone parts to be fixed and then screws in the bone screws 6. Sincethe plain washer can be displaced, adjustment of the screwing positionis possible before screwing down.

The embodiment shown in FIGS. 5 and 6 is, as far as the plate 2 isconcerned, identical to the embodiment shown in FIGS. 1 to 4. However,in this embodiment the bone screw 60 is different. Bone screw 60 has afirst thread shank section 61 with a bone thread and an adjoining secondthread shank section 62 with an M-thread. The diameter of the secondthread section 62 is smaller than the inner diameter of the plain washer20, so the second thread section 62 can be guided through the plainwasher 20 constructed like a sleeve. At its end opposite the tip of thebone screw the bone screw has a hexagonal recess, not shown, forbringing into engagement with a screwing-in tool for screwing the bonescrew into the bone.

In this embodiment the head of the screw 60 is formed by a separate nut63, which is shaped in the form of a spherical segment with a radiuscorresponding to that of section 22, shaped as a hollow sphericalsegment, of the plain washer 20. The nut 63 has on its upper side facingaway from the part shaped as a spherical segment a means 64, such ase.g. slits, for bringing into engagement with a screwing-in tool.

In operation again first the plain washer or the plain washers 20 is/areguided into the recesses 5 of the plate 2 and secured against fallingout via the screw 10. During the operation first the plate 2 is heldagainst the bone parts to be fixed and the screwing in position for thebone screws marked. Then the bone screws 60 are screwed in and the plate2 with the recesses 5 placed over the second thread section 62projecting from the bone. Then the nut 63 is screwed on to the secondthread section until it comes to rest in section 22, shaped as a hollowspherical segment, of the plain washer 20, wherein, owing to thespherical sections of the plain washer 20 and the nut 63, angles of thebone screw are possible in a predetermined range of angles.

The embodiment shown in FIGS. 7 and 8 differs from the embodiments shownin FIGS. 5 and 6 in that on the outer end of section 22, shaped as ahollow spherical segment, the plain washer 20 has an edge 24, projectinginwards by a predetermined measurement, encircling the inserted nut 63,starting from its upper side, by a predetermined measurement, so the nut63 is secured against falling out.

In operation with this embodiment the plain washer 20 is prefabricatedwith the nut 63 already inserted and, as with the previously describedembodiments, is first inserted into the plate 2 and secured againstfalling out with the securing screw 10. Further operation is as with theembodiment shown in FIGS. 5 and 6. This embodiment has the advantagethat the nut 63 is held and thus cannot be dropped by the surgeon duringthe operation.

In the embodiment shown in FIGS. 9 and 10 the connecting element betweenthe plate and the bone screw is constructed as a nut 30, instead of as aplain washer, for screwing on to the second thread shank section 62 ofthe bone screw 60. The nut 30 has a first area 31, corresponding in itsdimensions to the hollow-cylindrical central part 21 of the plain washerof the previous embodiments, but has an inner thread. Bordering on oneend of this central section the nut 30 has a head section 32 with anouter diameter, which, as with the plain washer 20, is slightly smallerthan the diameter of the indentation 7 but larger than the diameter d₂of the second area 5 b of the recess 5. Bordering on the other end ofthe central area 31, as with the plain washer, a ring-shaped projection33 is provided. The nut 30 additionally also has on its upper side means34, such as e.g. slits, for engaging with a screwing-in tool.

In this embodiment the bone screw 60 is provided with a shoulder 65,arranged between the bone thread shank section 61 and the thread shankcutout 62 with the M-thread, which shoulder is formed, for example, as aring-shaped projection and serves as a stop during screwing in, asillustrated in particular in FIG. 10.

In operation the bone screw or bone screws 60 is/are screwed in at thepreviously determined positions and then the plate with the recesses 5is placed over the thread sections 62 and then the nut 30 screwed on.

In the embodiment shown in FIG. 11 the bone screw of the bone threadshank section is constructed as hollow and provided with two oppositelongitudinal slits 66. Further provided is an expanding element, notillustrated in the figure, on the inside of the shank, which can beactuated in such a way that the shank sections formed by thelongitudinal slits 66 can be expanded apart. After the bone thread shanksection has been screwed in an expanding effect is thus achieved, whichguarantees an improved hold.

In the embodiment illustrated in FIG. 12 the plate 200 is constructed inparticular for application in cervical vertebrae stabilisation and hason each end 3, 4 in each case two recesses 5, wherein in each case twoadjacent recesses 5 share a securing screw 10. For this purpose the axisof the bore 8 for the securing screw 10 is arranged on the centrallongitudinal axis D and the dimension of the screw head 11 and theposition of the bore are chosen in such a way that in the screwed instate the screw head 11 engages in both indentations 7 of the adjacentrecesses 5. The plate 200 is further constructed as waisted.

The embodiments described can be combined on a plate in any way or thescrews, depending on the purpose, can be used for the variousembodiments, guaranteeing a modular system with great versatility.

Instead of the securing screw 10, a different securing element can beprovided, for example a spring element attached to the plate, which isbent away for inserting the plain washer 20 or the nut 30 and then snapsback to limit the cross-section of the recess.

The term plate is to be understood also to include elements with a notcompletely flat, for example a bent or in some other way curved,surface.

The device according to the invention can be not only applied tostabilising cervical vertebrae, but is also suitable for the externalfixing of broken bones, e.g. tubular bones.

1. A fixing device for bones comprising: a plate having a recess passingcompletely through the plate along a first axis, the first axis pointingin both a first direction and a second direction opposite to the firstdirection, wherein the recess is elongated in a direction transverse tothe first axis and the recess has a first area and a second area thatadjoin each other in the direction transverse to the first axis; aconnecting element defining a bore passing completely through theconnecting element along a bore axis, the connecting element having awall around the bore and a projection extending radially outward fromthe wall relative to the bore axis; a bone screw configured to bescrewed into a bone, the bone screw having a tip configured to passcompletely through the recess of the plate; wherein the second area ofthe recess of the plate is sized to permit insertion of the projectionof the connecting element completely through the plate in the firstdirection of the first axis and wherein the first area of the recess ofthe plate is sized to prevent removal of the projection completelythrough the plate in the second direction of the first axis; wherein,after the projection of the connecting element is inserted completelythrough the recess in the first direction of the first axis, the wall ofthe connecting element is movable in the recess in the directiontransverse to the first axis, from a first position in the second areawherein the connecting element is completely removable from the recessin the second direction of the first axis, to a second position in thefirst area wherein the element is not removable from the recess in thesecond direction of the first axis.
 2. The fixing device according toclaim 1, further comprising a securing device to secure the connectingelement in the recess, the securing device mountable to the plate toprevent removal of the connecting element from the recess.
 3. The fixingdevice according to claim 2, wherein the securing device comprises ascrew having a head, the screw being structured and arranged such that,when fixedly threaded into the plate, the head of the screw overlaps thesecond area of the recess to such an extent that it prevents theconnecting element from removal.
 4. The fixing device according to claim2, wherein the first area has a first diameter and the second area has asecond diameter, and wherein the securing device comprises a securingelement that overlaps the second area of the recess in the directiontransverse to the first axis to prevent removal of the connectingelement from the recess.
 5. The fixing device according to claim 4,wherein the connecting element has a first end and a second end, thefirst end having the projection extending radially outward from the wallrelative to the bore axis, the projection having an outer diameter thatis larger than the first diameter of the first area of the recess andthat is smaller than the second diameter of the second area and whereinthe connecting element has an outer diameter at the second end of theconnecting element that is larger than the second diameter of the secondarea.
 6. The fixing device according to claim 1, wherein the connectingelement comprises an annular seat that is structured and arranged toreceive a head of the bone screw, the head situated on a second endopposite from a first end defined by the tip of the bone screw.
 7. Thefixing device according to claim 6, wherein the head of the bone screwhas a first spherical segment and the connecting element comprises ahollow second spherical segment for receiving the mating first sphericalsegment of the head of the bone screw.
 8. The fixing device according toclaim 1, wherein the bone screw comprises a head and a shaft portion,the head of the bone screw comprising a nut removably attachable to theshaft on a second end opposite from a first end defined by the tip ofthe bone screw.
 9. The fixing device according to claim 8, wherein theconnecting element has an edge projecting into the bore of theconnecting element so that the nut is secured against falling out of theconnecting element.
 10. The fixing device according to claim 1, whereinthe connecting element is constructed as a nut with inner threads to bescrewed on to the bone screw on a second end opposite from a first enddefined by the tip of the bone screw.
 11. The fixing device according toclaim 1, wherein the bone screw comprises a shaft section having a bonethread and a head integral with the shaft section on a second endopposite from a first end defined by the tip of the bone screw.
 12. Thefixing device according to claim 1, further comprising a nut, whereinthe bone screw comprises a first shaft section adjacent the tip having abone thread and a second shaft section having a nut thread for threadingto the nut when the bone thread is screwed into a bone.
 13. The fixingdevice according to claim 12, wherein the bone screw further comprises ashoulder between the first shaft section and the second shaft section.14. The fixing device according to claim 1, wherein the tip of the bonescrew comprises a slit.
 15. The fixing device according to claim 1,wherein the plate further comprises an indentation in a surface of theplate around the recess.